Appendix 1: Plant species combinations in the complex environment.; Appendix 2: Age range, average and standard deviation of all species per treatment.; Appendix 3: Central brain volumes of all species per treatment. The central brain (CBR) volume in μm<sup>3</sup> of all species for all treatments: a) <i>A. io</i>, b) <i>A. urticae</i>, c) English <i>P. c-album</i>, d) Swedish <i>P. c-album</i>. Treatment <i>Newly eclosed</i> is depicted as a horizontal baseline, with grey lines on either sides representing the standard error. Filled points are significantly larger than the <i>Newly eclosed</i> treatment, and open points are not. Note that the lines between treatment-points do <i>not</i> indicate time series, but rather visualize the reaction norm of the connected treatments. (ANOVA and post hoc Tukey test).; Appendix 4: Antennal lobe volumes of all species per treatment. The relative antennal lobe (rAL) volume in μm<sup>3</sup> of all species for all treatments: a) <i>A. io</i>, b) <i>A. urticae</i>, c) English <i>P. c-album</i>, d) Swedish <i>P. c-album</i>. Treatment <i>Newly eclosed</i> is depicted as a horizontal baseline, with grey lines on either sides representing the standard error. Filled points are significantly larger than the <i>Newly eclosed</i> treatment, and open points are not. Note that the lines between treatment-points do <i>not</i> indicate time series, but rather visualize the reaction norm of the connected treatments. (ANOVA and post hoc Tukey test).; Appendix 5: Absolute mushroom body calyx volumes of all species per treatment. The absolute mushroom body calyx volume in μm<sup>3</sup> of all species for all treatments: a) <i>A. io</i>, b) <i>A. urticae</i>, c) English <i>P. c-album</i>, d) Swedish <i>P. c-album</i>. Treatment <i>Newly eclosed</i> is depicted as a horizontal baseline, with grey lines on either sides representing the standard error. Filled points are significantly larger than the <i>Newly eclosed</i> treatment, and open points are not. Note that the lines between treatment-points do <i>not</i> indicate time series, but rather visualize the reaction norm of the connected treatments. (ANOVA and post hoc Tukey test; * p < 0.05, *** p < 0.001).; Appendix 6: Linear regression analysis of rMB volume against rAL volume. Linear regression analysis of relative mushroom body calyx (rMB) volume in μm<sup>3</sup> against relative antennal lobe (rAL) volume for all species, all treatments combined. Open circles = <i>A. urticae</i>, filled black circles = <i>A. io</i>, filled grey circles = Swedish <i>P. c-album</i>, crossed circles = English <i>P. c-album</i>, p < 0.0001, R<sup>2</sup> = 0.26.